Agriculture Reference
In-Depth Information
biochemical methods is used to prepare the nanomaterial. For example, in a patent
by He, top-down methods such as grinding and crushing are used to bring raw plant
materials down to about 500 nm particles. Then, biochemical fermentation is used
to give the final nanoscale product. This fertilizer is claimed to lead to improved
yields and disease resistance (He
2008
). In another example, ammonium humate,
peat, and other additives are first ground down to micron size, then the mixture is
exposed to biochemical reactions, followed by further grinding to yield their
nanoscale product (Wu
2005
).
One interesting group of fertilizer nanoparticles is prepared by incorporating the
input into an emulsion that creates nanosized colloids or droplets. (Note that nano-
emulsions could equally be classified under Category 3, “nanoscale host mate-
rials.”) For example, a process has been patented where paper manufacturing
sludge, phosphate, magnesium, and ammonium salts are mixed with cellulose to
form nanoscale micelles. They also prepared nanoscale particles of similar compo-
sition using physical methods. Both are claimed to be efficient fertilizer treatments
(Inada et al.
2007
). Emulsification followed by polymer coating and high-speed
shearing has been used to prepare nanoparticles of ammonium chloride, urea, and
other components (Lin
2008
). Other materials have also been used to form fertilizer
nanoparticles. Pectin, a structural heteropolysaccharide contained in the primary cell
walls of plants, has been used to prepare fertilizer nanoparticles (Nonomura
2006
).
Micronutrients have also been incorporated into nanoparticle form in an effort to
improve uptake. Several examples fall under Category 1, although in certain cases,
these materials could also fall under Category 2 if they are described as nanoscale
additives for a bulk NPK fertilizer. Zinc and selenium, for example, are nutrients
that can be effectively provided to humans via micronutrient fertilization of crops
(Bell and Dell
2008
). A patent (He et al.
2009
) and several publications have
investigated the use of ZnO nanoparticles on a variety of crops such as cucumber
(Zhao et al.
2013
), peanuts (Prasad et al.
2012
), sweet basil (El-Kereti et al.
2014
),
cabbage, cauliflower, tomato (Singh et al.
2013
), and chickpea (Pandey et al.
2010
).
Figure
2.4
shows a TEM image of nano-ZnO applied to peanut seeds, resulting in
greater seed germination, seedling vigor, and chlorophyll content, as well as
increased stem and root growth. Overall, a higher crop yield was achieved, even
at a 15
lower concentration than a chelated ZnSO
4
addition (Prasad et al.
2012
). In
another study, foliar application of ZnO combined with laser irradiation with red
light led to enhanced yield compared to the nanoparticles alone (El-Kereti
et al.
2014
). This suggests that exploiting the unique electronic properties of
nanoparticle nutrient formulations could be an effective strategy. Another study
examining a variety of crops noted that nano-ZnO increased seed germination while
a bulk form of ZnO used for comparison had a negative impact on germination. The
nano-treatment increased pigments, protein and sugar contents, and nitrate reduc-
tase activities, and other antioxidant enzyme activities were increased (Singh
et al.
2013
). In a study on chickpeas exposed to nano-ZnO (20-30 nm), in addition
to increased seed germination and root growth, higher levels of a plant growth
hormone, indoleacetic acid (IAA), were observed (Pandey et al.
2010
). Interest-
ingly, while several studies have demonstrated the positive effects of nano-ZnO on
